G.1 General

23.2923GPPIP Multimedia Subsystem (IMS) centralized servicesRelease 17Stage 2TS

An MSC enhanced for ICS may support the Combined CS Access Authentication procedure. This procedure enables to authenticate and register all users accessing a network via CS access within the IMS domain as the only service domain. When this is done this annex is used instead of clause 7.2.1.1.

If the MSC enhanced for ICS supports the Combined CS Access Authentication all users within this MSC domain shall be authenticated utilizing this procedure.

The main additional function of MSC Server enhanced for ICS is:

– Receiving 3G CS authentication parameters from the S-CSCF.

Other functions are similar with the existing MSC Server enhanced for ICS, e.g. Controls the MGW functions described in TS 23.002 [3] to enable the interworking between CS access and RTP bearers.

In this solution, the IMS will perform authentication procedure as normal IMS registration.